Miscellaneous · course 105 of 105

Atoms In, Grams Out: Chemistry by the Mole

Do the counting side of intro chemistry: atoms in a formula, balancing equations, molar mass, grams to moles and back, the limiting reactant, theoretical yield and mass percent.

4 modules

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What it teaches

The counting side of introductory chemistry. The words (atom, molecule, mole, the Avogadro constant’s exact value, molar mass, the law of conservation of mass, a balanced equation, coefficient versus subscript, limiting reactant, theoretical yield), counting the atoms in a formula (subscripts, a number in front, brackets), balancing an equation in the smallest whole numbers, molar mass from a printed table of atomic weights, grams to moles and back, mole ratios from a balanced equation, the limiting reactant, theoretical yield in grams, and the mass percent of an element in a compound. The AI asks 3 questions, places you, shows a short card per module, then gives you one question at a time.

For high-school and early-college chemistry students who can follow the steps in class but want drill on the arithmetic. Not a lab course, and it can’t judge whether a real reaction works or is safe.

How long

40 items (10 concept questions and 30 drills). A student who already knows it answers intake questions 2 and 3 and does 10 check rounds, then the 12-item final. For a beginner, a coded copy of the tutor’s rules played a simulated beginner (misses intake question 2, then misses a fixed share at random): a median of 20 rounds to pass all four modules with no further misses, 24 with 1 miss in 10, 34 with 1 in 5 and 69 with 1 in 3 (about 40 to 120 across runs), then the 12-item final. That is 1-4 sessions; a rough simulation, not timed with a real student. The tutor gives a one-line save code at the end of each session.

From the answer key · M1, row A9

Balance C3H8 + O2 → CO2 + H2O. Give the coefficients in order, as the smallest whole numbers.

Think first, then show the answer

Answer1, 5, 3, 4

WorkingC3H8 + 5 O2 → 3 CO2 + 4 H2O. Atoms, left | right: C 3 | 3; H 8 | 8; O 10 | 10. Only the coefficients change, never a subscript.

The wrong answer it catches1, 3, 3, 4 → C and H are balanced but O isn’t (6 on the left, 10 on the right).

Balanced means equal counts: “each side of the chemical equation must represent the same number of atoms of any particular element”. “An equation adhering to these requirements is said to be balanced.”
Worked example: Li + N2 → Li3N. N is 2 on the left and 1 on the right, so put 2 in front of Li3N. Now N is 2 | 2 but Li is 1 | 6, so put 6 in front of Li. The coefficients are 6, 1, 2.

The modules

4 modules, drilled one item at a time.

M0
Words and ideas
The words: atom, molecule, mole, the Avogadro constant, molar mass, conservation of mass, balanced equation, coefficient and subscript, limiting reactant, theoretical yield
M1
Atoms in a formula and balancing equations
Count the atoms in a formula (brackets too) and balance an equation in the smallest whole numbers
M2
Molar mass, grams and moles
Molar mass from a table of atomic weights, grams to moles and moles to grams
M3
Reactions: mole ratios, limiting reactant, yield, percent composition
Mole ratios, the limiting reactant, theoretical yield in grams, and the mass percent of an element

Before it teaches, it asks

1
What are you studying chemistry for (a school class, college, an exam, or just curious), and which part is hardest so far: counting atoms, balancing, moles, or reaction calculations?
2
Balance H2 + O2 → H2O. Give the coefficients in order, as the smallest whole numbers.
3
A substance has a molar mass of 40.0 g/mol. How many moles are in 100.0 g of it? Give the moles to 2 decimal places.

What’s exact, and what isn’t

Show

Straight from the course’s own notes.

Words (M0): Quoted word for word on the cards from NIST’s page “SI Units – Amount of Substance” (updated 11 August 2026 per the page), NIST’s CODATA page for the Avogadro constant (2022 CODATA values) and nine Wikipedia articles (CC BY-SA, short quotes), all read 2026-10-13. The 10 Answers are plain-words versions of those quotes, not quotes. A script checks all 33 quotes on saved copies of the pages (it does not re-fetch them); they also matched the live pages on 2026-10-13.
The Avogadro constant: One mole contains exactly 6.02214076 × 10²³ elementary entities (NIST). The CODATA page gives 6.022 140 76 × 10²³ per mole with the standard uncertainty “(exact)”. On both pages the power of ten is a superscript; the saved text flattens it to “1023”, and the cards say so.
Atomic weights (M2, M3): The 11 elements in the course (H, C, N, O, Na, Mg, Al, S, Cl, Ca, Fe) come from CIAAW’s “Abridged Standard Atomic Weights 2024”, as printed (for example H 1.0080, O 15.999, S 32.06). The M2 card prints the table, and every M2 and M3 question that needs atomic weights lists the ones to use, copied from that table, so every key uses those numbers exactly. These are abridged values (the page: “quoted to five significant figures unless such precision cannot be attained”), and other periodic tables print some of them differently, so a student who ignores the numbers in the question and works from another table can get different last digits.
Computed by script: Every M1, M2 and M3 key. Atoms are counted by a formula parser (brackets, a number in front). Balance keys come from an exact solve over fractions, scaled to the smallest whole numbers (the answer must be unique and positive). M2 and M3 keys are exact fractions rounded half-up to the decimal places each question names; a script fails if a value sits exactly on a rounding tie. The limiting reactant is found by comparing the product each reactant could make, and cross-checked a second way.
Wrong answers: All 26 listed wrong answers are checked by a script to be wrong and to equal what the slip they name gives (ignoring the number after a bracket, the ratio upside down, the reactant with fewer grams, and so on).
Rounding check: For the 12 M2 and M3 items that turn grams, moles or percentages into a number, a script also recomputes the answer with molar masses rounded to 2 decimals and with a 2-decimal atomic-weight table, and fails if the answer at the asked places changes. It checks those two alternatives only, not every table a student might use. The four molar-mass items are exact sums of the numbers given in the question.
Honest limits: The course drills the quoted definitions and the arithmetic; it can’t tell whether a real reaction will happen or is safe, and it isn’t connected to NIST, CIAAW or Wikipedia. Answers are given to a stated number of decimal places, not to significant figures. The equations in M3 are given balanced (balancing is drilled in M1).
Not in it yet: Moles to number of particles (it would need scientific-notation answers), percent yield, ions and charges, gases, solutions and molarity, empirical and molecular formulas from data, naming compounds, predicting products, oxidation numbers, acids and bases, energy changes, elements beyond the 11 on the card.